Method of destroying undesirable plants



3,020,146 METHOD OF DESTRUYWG UNDESIRAIBLE PLANTS Sidney B. Richter,Chicago, Ill, assignor to Velsicol gihemicai Corporation, Chicago, Ill.,a corporation of EEDHS No Drawing. Filed Sept. 22, 1958, Ser. No.762,237 Claims. (Cl. 71-26) This invention relates to new herbicidalcompositions of matter. More specifically, this invention relates to thecontrol of undesirable plant life with ot-chlorophenylacetic acid, itsanhydride, its amides, its esters, its alkali metal salts, or its aminesalts. a-Chlorophenylacetic acid, which has the structure 1 CHCOOH willhereinafter be referred to as Compound I. This chemical compound and itsderivatives as cited above have marked activity as herbicides useful forthe control of undesirable plant life.

Compound I can be obtained readily by heating mandelic acid to about 140C. with concentrated hydrochloric acid, by the action of caustic potashon trichloromethylphenylcarbinol, by the action of water on the acidchloride obtained from mandelic acid and phosphorus pentachloride, or bythe direct chlorination of phenylacetic acid. A racemic mixture isgenerally obtained. If it is desired to obtain either of the opticallyactive dor l-forrns, the racemic mixture can be resolved by thetechniques known in the art, such as with morphine. Alternately, thesynthesis can be made from the appropriately active mandelic acids.

The anhyride of Compound I is prepared by the removal of one molecule ofwater from two molecules of Compound I as the free acid. In practice, itis convenient to prepared the anhydride by the acylation of the freecarboxylic acid by its acid halide in the presence of a strong acylatingagent such as pyridine. Thus a mixture of dry pyridine and dry benzeneare treated with 1 mole of the acid chloride of Compound I. The slightlyexothermic reaction proceeds with the formation of an intermediatepyridinium salt. One mole of Compound I as the free acid is then added,the precipitate of pyridine hydrochloride is removed, and the anhydrideof Compound I is isolated by removal of the benzene.

The acid halide of Compound I required in the above and other synthesisis prepared by the reaction of the free acid with a phosphorus trihalidein the conventional manner. Thus the treatment of Compound I withphosphorus trichloride until the reaction ceases produces the acidchloride of Compound I.

Compounds which are salts, esters, or amides of Compound I can beprepared readily from the free acid. Thus treatment of the free acidwith ammonium hydroxide gives a product which is the salt ammoniumachlorophenylacetate. Similarly, an alkali metal salt of Compound I canbe made by the treatment of the free acid with bases, such as thehydroxides, of alkali metals. Treatment of the acid with sodiumhydroxide thus gives the salt sodium ot-chlorophenylacetate as theproduct, while the use of potassium hydroxide gives the salt potassiumet-chlorophenylacetate.

Amine salts of Compound I are prepared by the addition or" the free acidto various amines. Typical amines which can be used to prepared suchamine salts are di- 3,@Z,lii Patented Feb. 6, 1962 ICC 2 methylamine,trimethylamine, triethyla-mine, diethanolamine, tricthanolamine,isopropylamine, morpholine, and the like. The resulting products are,respectively, the dimethylamine, trimethylamine, triethylamine,diethanolamine, triethanolamine, isopropylamine, and morpholine salts ofa-chlorophenylacetic acid.

Esters of Compound I are prepared by the condensation of the acid withvarious alcohols. Thus the con densation of methyl alcohol with CompoundI gives the de sired ester, methyl ot-chlorophenylacetate. Other typicalalcohols which can be used are propyl, isopropyl, n-butyl, sec-butyl,isobutyl, text-butyl, amyl, hexyl, heptyl, octyl, nonyl, decyl, and thelike. The products are the corresponding alkyl esters ofa-chlorophenylacetic acid. Although such complex esters as thoseprepared by the esterification of Compound I with butoxyethanol,propylene glycol butyl ether, and the like are useful products inaccordance with this invention, preferred esters are those in which theesterifying group is an unsubstituted alkyl group which contains from 1to 10 carbon atoms. The condensation of the acid with the alcohol iscarried out suitably in an inert solvent such as an aromatic hydrocarbonand in the presence of a few percent by weight of an acid catalyst suchas p-toluenesulfonic acid. The water which forms during theesterification reaction can be removed continuously in many cases fromthe reaction mixture by distillation as it forms, and its volume can bemeasured to determine when the esterification is complete. The ester isthen isolated by distillation of the inert solvent.

Amides of Compound I can be prepared conveniently by the reaction of theacid halide of Compound I with ammonia or various amines. The reactioncan be carried out in an inert solvent such as ether or benzene.Preferably two moles of the amine are used for each mole of the acidhalide employed, since the hydrogen halide released during the reactionis taken up by some of the free amine which remains. The simplest amide,a-chlorophenylacetamide, can be prepared by the reaction of the acidchloride of Compound I with ammonia, either as the free gas or as anaqueous solution. This amide can also be prepared by hydrolysis of thecorresponding nitrile. Substituted amides are prepared by the reactionof the acid halide of Compound I with amines such as any of the primaryor secondary amines suggested above for the preparation of the aminesalts of Compound I. Thus, for example, the reaction of the acidchloride of Compound I with methylamine, butylamine, decylamine, ordiethylamine gives the Nmethyl-, N- butyl-, N-decyl-, orN,N-diethyl-a-chloroacetamides, respectively. While more complex aminessuch as the aromatic amines can be used as the amine reactant to givedesirable products, which are specifically named as anilides, preferredamine reactants are alkylamines containing up to 10 carbon atoms.

For practical use as herbicides, the compounds of this invention areformulated with inert carriers to obtain proper concentrations and tofacilitate handling. For example, these compounds can be formulated intodusts by combining them with such inert substances as talc or clays. Thealkali metal salts of Compound I are particularly suited to such dustformulations, and dusts containing from 5 to 25 percent by weight ofactive compound are convenient for use in the field. The. compounds ofthis invention, however, are preferably applied as sprays. These can bemade as simple solutions by dissolving the compounds in organic solventssuch as xylene, kerosene, or the methylated naphthalenes. The esters ofCompound I, which ordinarily are liquids at room temperature, areparticularly suited to formulation by this method. The amine salts ofCompound I often show good solubility in water and can be used directlyas aqueous solutions.

The compounds of this invention can also be emulsified or suspended inwater by the addition of emulsifiers and wetting agents. Theformulations of these active herbicidal compounds are either applieddirectly to the plants to be controlled, or the soil in which the plantsare growing can be treated. Substances such as other pesticides,stabilizers, activators, synergists, spreaders and adhesives can beadded to the formulations if desired. There is no significant dilferencein effect from the amount of water or organic solvent for diluting theseherbicides, providing the same amount of chemical is distributed evenlyover a given area. Such distribution can be obtained, for example, withlow-pressure, low-volume sprays at the rate of about gallons of sprayper acre.

In applying the herbicidal compounds, consideration must be given to thenature and stage of growth of the crop, the species of Weed present, thestage of growth of the weeds, environmental factors influencing the rateand vigor of the weed growth, weather conditions at the time ofapplication and immediately following, and the dosage to be applied to agiven area. Weeds are most susceptible when they are small and growingrapidly. Early application, therefore, results in better control withless chemical and increased yields because of the early destruction ofthe competing weeds. The larger and older the weeds the higher theconcentration needed to kill them. Summer annuals such aslambs-quarters, pigweeds, cocklebur, and sunflower should be sprayedwhen they are less than 4 inches high. Winter annuals such as variousmustards, fan-weed, yellow star-thistle, and wild radish are most easilykilled while they are still in the rosette stage. Usually weeds growingrapidly under optimum conditions are relatively susceptible, whereasthose growing under adverse conditions tend to be resistant to theherbicide sprays.

The eflfectiveness of the compounds of this invention in smallquantities makes them economically sound for weed control on largeareas, with a great saving in labor and cost, in addition tocorresponding crop increases. These compounds are particularly valuablein weed control because they are harmful to many weeds but harmless orrelatively harmless to some cultivated crops. Minute quantities incontact with plant tissues may be absorbed and translocated to all partsof the plant, causing striking changes in the form and functions andoften resulting in their death. The actual amount of compound to be useddepends on a variety of factors but is influenced primarily by thespecies of undesirable plant to be controlled. Thus while fractions of apound of actual Cornpound I or its equivalent of an ester, salt, amide,or the anhydride of Compound I are often sufilcient for postemergenceweed control on an acre of corn, seed flax, perennial grass seed crops,pastures or grazing areas (without legumes), wheat, and the like, theparticular species of weeds encountered in evergreen and deciduousdormant nursery stock, nursery conifers, waste areas, woody brush, andthe like may require the use of one or more pounds of Compound I or itsderivatives per acre for good control. Dosage adjustments with thelow-volume, low-pressure applications suggested can be made by changingthe nozzle size, nozzle spacing, pressure, or traveling rate of thespray equipment.

The manner in which the herbicidal compounds of this invention can beprepared and utilized is illustrated in the following examples:

EXAMPLE I Preparation of mandelic acid Mandelic acid(ot-hydroxyphenylacetic acid) is prepared, for example, as described inOrganic Syntheses, Collective Vol. I, p. 336 (1941) by the hydrolysis ofmandelonitrile obtained from benzaldehyde and hydrogen cyanide.

t EXAMPLE 2 Preparation of m-chlorophenylacetic acid (Compound I)Mandelic acid g.) and phosphorous pentachloride (250 g.) are placed in a500 ml. round-bottomed flask fitted with an internal thermometer and anefficient stirrer. The mixture is stirred gently and heated at 100 C.for 4 hours. -The temperature is then increased to C. for 1 hour. Theproduct is then distilled in vacuo, and the fraction boiling at 124 to126 C. at 45 mm. pressure is treated carefully with cold water to givecrystals, which are filtered, pressed dry, and dried completely in avacuum oven to give the desired oc-ChlOIO phenylacetic acid, meltingpoint 78 C.

EXAMPLE 3 Preparation of the sodium salt of Compound I Compound I (0.5mole) is dissolved in 500 cc. of methanol and treated with a solution ofsodium hydroxide (20 g.; 0.5 mole) in 100 cc. of methanol. The methanolis removed by distillation in vacuo on the steam bath, and the solidresidue is slurried with 100 cc. of cold, dry ether, filtered, presseddry, and dried completely in a vacuum oven to give the desired sodiumsalt of Compound 1.

EXAMPLE 4 Preparation of the ammonium salt of Compound 1 Treatment ofCompound I (0.5 mole) in 500 cc. of methanol with 34 cc. of commercialconcentrated ammonium hydroxide according to the method given in theprevious example gives the desired ammonium salt of Compound 1.

EXAMPLE 5 Preparation of the dimethylamine salt of Compound I Compound 1(0.5 mole) is dissolved in 500 cc. of dry ether and treated withdimethy-lamine (22.5 g.; 0.5 mole). The solid which separates isfiltered, washed twice with 100 cc. portions of cold ether, filtered,pressed dry, and dried completely in a vacuum oven to give the desireddimethylamine salt of Compound 1.

EXAMPLE 6 Preparation of the diethanolamine salt of Compound I In themanner described in the previous example, Compound I (0.5 mole) istreated with diethanolamine (52.5 g.; 0.5 mole) in 500 cc. of dry ether.The product which is isolated is the diethanolamine salt of Compound I.

EXAMPLE 7 Preparation of the morpholine salt of Compound I Compound I(0.5 mole) is treated with morpholine (43.5 g.; 0.5 mole) in 500 cc. ofether, and the product is worked up as described for the preparation ofthe dimethylamine salt to give the desired morpholine salt of CompoundI.

EXAMPLE 8 Preparation of the ethyl ester of Compound 1 Compound I (0.5mole), ethyl alcohol (23 g.; 0.5 mole), and 3.0 g. of p-toluenesulfonicacid are dissolved in 500 ml. of benzene, and the solution is placed ina 1 liter, round-bottomed flask fitted with a reflux condenser and acalibrated Dean-Stark tube. The solution is heated at reflux temperatureuntil 9 cc. of water have been collected in the Dean-Stark tube. Thecooled reaction mixture is then extracted twice with SO-cc. portions of10% sodium carbonate solution, and filtered. The benzene is distilledofi in vacuo on the steam bath, and the residue is then distilled invacuo to give the desired ethyl ester of Compound I.

EXAMPLE 9 Preparation of the decyl ester of Compound I In the manner andapparatus described in the previous example, Compound I (0.5 mole) andnormal primary decyl alcohol (79 g.; 0.5 mole) are refluxed in 500 ml.of benzene in the presence of 3.0 g. of p-toluenesulronic acid until 9cc. of water have been distilled from the reaction mixture. Work-up ofthe reaction mixture as described in the previous example gives thedesired decyl ester of Compound I.

EXAMPLE 10 Preparation of the n-butyl ester of Compound I The reactionof Compound I (0.5 mole) and n-butyl alcohol (37 g.; 0.5 mole) by themethod described above for the preparation of the ethyl ester is used toprepare the n-butyl ester of Compound I.

EXAMPLE 11 Preparation o] the acid chloride of Compound I Compound I (1mole) is placed with 500 cc. of dry benzene in a 2-liter, l t-necked,round-bottomed flask fitted with a mechanical stirrer, reflux condenser(calcium chloride tube), and dropping funnel. Phosphorus tn'chloride(123 g.; 0.9 mole) is added slowly dropwisc with vigorous stirring whilethe reaction flask is cooled with cold water if necessary to control thereaction. When all the PCl has been added and the evolution of hydrogenchloride has ceased, the reaction mixture is then transferred todistillation apparatus, and the solvent is distilled off. The residue isthen distilled in vacuo to give the desired acid chloride of Compound I.

EXAMPLE 12 Preparation of. the amide of Compound I One mole of the acidchloride of Compound I is placed with 500 cc. of dry benzene in a1-liter, B-necked flask fitted with a reflux condenser, mechanicalstirrer, and a gas inlet tube having a sparger tip. The mixture isstirred While dry ammonia gas is, passed into the mixture for severalhours. When the ammonia gas is no longer taken up, the precipitated saltis filtered ofii and extracted twice with 100 ml. portions of ether. Theether extracts and benzene filtrate are dried over magnesium sulfate andfiltered, and the solvents are distilled ofi to give the desired amideof Compound I.

Example 13 Preparation of the N-n-decylamide of Compound I One mole ofthe acid chloride of Compound I and 500 ml. of dry benzene are placed ina 2-liter, 3-necked, roundbottom flask fitted with a mechanical stirrer,reflux condenser, internal thermometer, and dropping funnel. n-Decylamine (314 g.; 2.0 moles) in 250 ml. benzene is added dropwise withvigorous stirring. When all the amine has been added, the reactionmixture is refluxed for 2 hours and cooled, after which the precipitatedsalt is filtered oft and extracted with two 100 ml. portions of ether.The ether extracts and benzene filtrate are dried over magnesium sulfateand filtered. Distillation of the solvents gives the desiredN-n-decylamide of Compound I.

EXAMPLE 14 Preparation of the N,N-diethylamide of Compound 1 One mole ofthe acid chloride of Compound I is treated with diethylamine (146 g.;2.0 moles) in the manner and apparatus described in the previous exampleto give the N,N-diethylamide of Compound 1.

EXAMPLE 15 Preparation of the anhydride Compound 1 Dry pyridine (158 g.;2.0 moles) and 1 liter of dry benzene are placed in a 2-liter, 3-necked,round-bottom flask fited with a dropping funnel, mechanical stirrer,reflux condenser, and internal thermometer. One mole of the acidchloride of Compound I, which is prepared as described in a previousexample, is added rapidly with stirring to the reaction mixture.Compound I (1 mole) is then added in portions over a period of about 10minutes with rapid stirring. The pyridine hydrochloride whichprecipitates is filtered off, and the benzene is distilled from thefiltrate in vacuo. The residue contains the desired anhydride ofCompound I, which can be purified by crystallization from a suitablesolvent.

EXAMPLE 16 Preparation of an emulsifiable concentrate of Compound I Thefollowing concentrate is prepared by mixing the ingredients intimatelyin the given percentage proportions by weight:

Percent Compound I 25 Antarox A-400 40 Methanol 35 Antarox A-400 is thetrade name under which a nonionic detergent of the aromatic polyethyleneglycol ether type is sold. The above concentrate is diluted with waterto the desired concentration for use.

EXAMPLE 17 Preparation of an emulsifiable concentrate of the n-butylester of Compound I The following ingredients are mixed thoroughly inthe given percentage proportions by weight:

Triton X-100 is the trade name under which an emulsifier of the alkylaryl polyether alcohol type is sold. The above concentrate is dilutedWith water to the desired concentration for use.

EXAMPLE 18 Preparation of a dust from the sodium salt of Compound I Thesodium salt of Compound I (10% by weight) and talc by Weight) arecombined and ground to the desired particle size in a mechanicalgrinder-blender.

The herbicidal activity of chemical compounds is often demonstrated bythe ability of the chemicals to kill or arrest the growth of tomatoplants. The tomato plant is readily grown and maintained under uniformconditions for experimental purposes in greenhouses, and its response tochemicals is very similar to that observed for a wide variety ofeconomically important species of undesirable plant life in the field.

The herbicidal activity of the compounds of this invention, for example,can be demonstrated in greenhouse experiments on young potted tomatoplants (Bonny Best variety). The compounds are formulated into 10percent wettable powders and are dispersed in water at a concentrationof 2,000 parts per million actual chemical. Ten milliliters of analiquot portion of the dispersion is added to the soil surface of thetomato plants, approximately 5 to 7 inches tall. In order to avoid undueconcentration of accumulation of the chemical in any given area, 5 holesthe size of a pencil and about 1 inch deep are punched in the soilsurface around the shoot, and the 10 milliliter application is dividedequally among the 5 holes. Three plants are used for each application.The treated plants are held under greenhouse conditions for 7 days,provided with subterranean watering, and observed for response totreatment. The results indicate a high order of herbicidal toxicity ofthe compounds of this invention.

I claim:

1. A method of destroying undesirable plants which comprises contactingsaid plants with a herbicidal composition comprising an inert carrierand as the essential active ingredient, in a quantity which is injuriousto said plants, a compound selected from the group consisting ofalpha-chlorophenylacetic acid, its esters in which the esterifying groupis an unsubstituted alkyl group containing from one to ten carbon atoms,its alkali metal salts, its anhydride, its amine salts in which theamine component contains up to ten carbon atoms, and its amides in whichthe amine component contains up to ten carbon atoms.

2. A method as described in claim 1, wherein the compound is an alkalimetal salt of alpha-chlorophenylacetic acid.

3. A method as described in claim 1, wherein the compound is an aminesalt of alpha-chlorophenylacetic acid in which the amine componentcontains up to ten carbon atoms.

4. A method as described in claim 1, wherein the compound is an ester ofalpha-chlorophenylacetic acid, in which the esterifying group is anunsubstituted alkyl group containing from one to ten carbon atoms.

5. A method as described in claim 1, wherein the compound is an amide ofalpha-chlorophenylacetic acid in which the amine component contains fromone to ten carbon atoms.

6. A method as described in claim 1, wherein the compound isalpha'chlorophenylacetic acid.

7. A method as described on claim 1, wherein the compound is sodiumalpha-chlorophenylacetate.

8. A method as described in claim 1, wherein the compound is thediethanolamine salt of alpha-chlorophenylacetic acid.

9. A method as described in claim 1, wherein the compound is N-butylalpha-chlorophenylacetate.

10. A method as described in claim 1, wherein the compound is his(alpha-chlorophenylacetic) anhydride.

References Cited in the file of this patent UNITED STATES PATENTS1,948,342 Dvornikofi Feb. 20, 1934 2,007,642 Simo July 9, 1935 2,394,916Jones Feb. 12, 1946 2,412,510 Jones Dec. 10, 1946 2,558,762 Korh et a1July 3, 1951 2,649,363 Swezey Aug. 18, 1953 2,843,470 Searle July 15,1958 OTHER REFERENCES Ghielmetti in Chemical Abstracts, vol. 47, 1953,col. 11161(i).

Dishart et al., in Chemical Abstracts, Vol. 50, 1956, col. 145210) to14522(b).

Preston et al., in Science, Vol. 119, Apr. 2, 1954, pages 437-438.

Wain et al.: The Chemistry and Mode of Action of Plant GrowthSubstances, Butterworths Scientific Publications, London, 1956, pages205-410.

Mitchell et al., in Science, col. 118, Oct. 30, 1953, pages 518-519.

1. A METHOD OF DESTROYING UNDESIRABLE PLANTS WHICH COMPRISES CONTACTINGSAID PLANTS WITH A HERBICIDAL COMPOSITION COMPRISEING AN INERT CARRIERAND AS THE ESSENTIAL ACTIVE INDREDIENT, IN A QUANTITY WHICH IS INJURIOUSTO SAID PLANTS, A COMPOUND SELECTED FROM THE GROUP CONSISTING OFALPHA-CHLOROPHENYLACETIC ACID, ITS ESTERS IN WHICH THE ESTERIFYING GROUPIS AN UNSUBSTITUTED ALKYL GROUP CONTAINING FROM ONE TO TEN CARBON ATOMS,ITS ALKALI METAL SALTS, ITS ANHYDRIDE, ITS AMINE SALTS IN WHICH THEAMINE COMPONENT CONTAINS UP TO TEN CARBONS ATOMS, AND ITS AMIDES INWHICH THE AMINE COMPONENT CONTAINS UP TO TEN CARBON ATOMS.